When the show began, Knight appeared visibly uncomfortable on stage, and opted to stand behind his fellow bandmates ---Donnie Walhberg, Joey McIntyre, Danny Wood and Jordan Knight— and answer text messages while the rest of the group executed their signature, synchronized choreography.

The group attempted to make Knight more at ease, repeatedly wrapping its arms around him, while the enthusiastic crowd offered their own cheers of encouragement.

When Jordan announced that his brother would sing on the next song, the ballad "Survive You" from their new album 10, Jonathan laughed, attempted to sing, stopped and then made his way off the stage. After the song, the band announced Knight would return, but as the band continued to preform their signature hits, including “Step By Step” and “Hangin’ Tough,” it became increasingly more clear that Knight would not be coming back onto the stage.

After the show, Knight made a simple post on his Twitter account: "I'm sorry ……"

Knight has been publicly open about his suffering with social anxiety, including a 2001 sit down with Oprah Winfrey.

Representatives from Clear Channel, which produced the show, confirmed the events to THR, but offered no further explanation for Knight's abrupt exit.

The morning after their iHeartRadio show, NKOTB made an appearance on Today, singing “We Own Tonight.” When the time came for Jonathan to sing his solo — a part that his bandmates had to sing for the night prior – he preformed without any issues.

Knight and the rest of NKOTB are now busy preparing for The Package Tour with fellow boy bands, 98 Degrees and Boyz II Men, which begins on May 31.